Gear differentials include compound planetary gear sets carried within a differential housing interconnecting a pair of output shafts for opposite directions of rotation with respect to the housing. An input shaft is connected to the housing for rotating the housing about a common axis of the output shafts. Sun gear members of the respective planetary gear sets, also referred to as "side" gears, are coupled to inner ends of the output shafts. Planet gear members of the planetary gear sets operatively connect the two side gears in a mutual driving relationship for relative rotation in opposite directions.
One known arrangement of such planetary gearing positions the side and planet gears within the housing for rotation about axes that extend parallel to each other. Differentials with this type of gearing arrangement are referred to as "parallel-axis" gear differentials. The planet gears of this type of differential are generally mounted in pairs within the differential housing. Preferably, the planet and side gears are provided with helical teeth; and one portion of each planet gear meshes with one of the side gears, while another portion of each planet gear meshes with its paired planet gear.
The invention herein relates to known designs of parallel-axis differentials in which the planet gears are individually supported for rotation within pockets formed in the housing. The planet gear pockets are shaped to mate with and provide (a) bearings for supporting the cylindrical outside diameter surfaces of the planet gears as well as (b) pocket end portions that act as thrust surfaces against which the end faces of the planet gears interact in response to the axial forces created when the helical teeth of the gearing are under load. The frictional resistance which results between the planet gears and their respective pockets is used to augment the desired "torque bias" of the differential. However, this same frictional resistance must be constantly controlled by adequate lubrication in order to avoid undesirable wear problems, and the relatively tight tolerances between the planet gears and their pockets make lubrication of their respective mating surfaces quite difficult.
Inadequate lubrication is a particular problem at those times when the vehicle has been parked or standing for an extended period just prior to the required operation of the differential. When parked or standing, lubrication drains away from the interfaces between the planetary gearing and the housing, and adequate lubricating fluid is usually not restored to these interfaces until some appreciable time after the vehicle is moving again. Therefore, differentiation at such times can cause excessive wear to the dry surfaces of these interfaces, particularly if the planetary gearing is subjected to relatively high loads. For instance, such high-torque loads occur when relatively high engine power is used at lower speeds, e.g., when accelerating a vehicle from a stopped condition and when turning sharply to leave a parking place.
The disclosed invention is specifically directed to overcoming such lubrication problems. In this regard, Japanese Application 300080110 (recently filed by the assignee of this application) discloses a multi-grooved washer specially designed for use in parallel-axis differentials, and a variation of that specially-designed washer is incorporated in preferred embodiments of our invention.